1. Field of the Invention
The present invention generally relates to tool changers for either manually operated or automated machine tools and, more particularly, to a tool changer which obtains and locks, as well as unlocks and positively ejects, tapered tool holders.
2. Description of the Prior Art
Considerable effort has been dedicated to the design of power assisted devices for the obtaining and securing of tapered tool holders in the spindles of machine tools. An increase in interest in and need for these devices has resulted from the large number of programmable machine tools with automatic tool changers currently in use.
Conventional vertical milling machines utilize a draw bar, threaded at one end, which when inserted into the tapped cavity of a standard tapered tool holder and rotated will seat the tool holder against the complementary surface of the spindle. A large number of existing designs of power assisted draw bars use hydraulic, pneumatic or electric motors to rotate the draw bars. While these power assisted devices are considerably quicker in operation than is a manual draw bar, additional rapidity is desirable. In general, these devices are noisy and slow since many incorporate an impact wrench approach. Automating these devices allows their use with automatic tool changers. However, occasional failures to engage the threaded draw bar when used with these automatic tool changers can result in dropped tool holders.
Alternative arrangements replace the foregoing rotary draw bar motion devices with one relying on axial motion, doing so by using locking fingers which contact and lock the tool holder. These also have several drawbacks, as these devices tend to be complicated and comprised of a large number of parts internal to the spindle. Spindles having the sizes required to contain these complex mechanisms are only found on larger machine tools. Further, some prevent translating the spindle to change depth of cut thus requiring a movable table to support the work piece. Finally, remachining of the spindle and/or tool holders is often required, necessitating disassembly and removal of the spindle when retrofitting a machine tool with a power draw bar. This greatly adds to the fabrication and installation cost of these devices. There also exist other designs which apply to a specific and unique machine tool design and are not adaptable to standard models.
Thus, there is a desire for a rapidly, but sure, operating tool changer. This changer should be able to be retrofitted to commercially available rotary action machine tools with little modification of same. Further, such a change should be at relatively low cost.